The proposed research will furnish new information on the control mechanisms of biomineralization. As the experimental system, shell regeneration in two species of Archaeogastropod molluscs, Tegula funebralis and Tegula ligulata, will be studied with X-ray and selected area (electron) diffraction, correlated with scanning and transmission electron microscopy. Regenerated material will be examined one hour to 48 days after a window has been cut in the shell and replaced with the appropriate substrate (either plastic film or dental wax). By allowing snails to regenerate on plastic film or on a transmission electron microscope grid pressed into dental wax, the same crystals can be identified mineralogically by X-ray and electron diffraction, and morphologically by scanning or transmission electron microscopy without alteration or destruction of the specimen. Using the method outlined above, the effects on biomineralization of two factors, a homogenate from the visceral ganglion of the snails, and ecdysterone, will be examined. The tissues directly involved in regeneration (mantle, foot, hepatopancreas) will also be observed with transmission electron microscopy during this phase of the study.